Television system



Sept. 10, 1929. HORTON 1,728,122

TELEVISION SYSTEM Filed April 6. 1927 2 Sheet sSheet 1 Arm/MU Sept. 10, 1929. J. w. HORTON TELEVISION SYSTEM Filed April 6, 1927 2 Sheets-Sheet 2 N m w wt Mlwwl Patented Sept. 10,

UNITED STATES PATENT OFFICE.

Joana w. noarou, or mum, raw mam, assrenoa 'ro nan. ramrnona momroams, mcoaromm. or new Yoax, n. Y., A coaroaa'rron or new roan.

rmnvmon srsnm,

Application filed April 6, 1987. Serial No. 181,570.

This invention relates to picture transmission and television systems, and especiall to electrical wave amplifying systems the field of application of which includes picture transmission and television, the general object of the invention being reduction of distortion.

- As a system for transmitting to a distance a pictorial representation of a subject, the embodiment of the invention herein chosen by way of example com specifically stated, means at the transmitting end of the system for rapidly scanning the subject point by point and producing by a photo-electric cell an electric current varymg in accordance with the light received from the successive elemental areas of the explored subject, and a transmission channel for amplifying and transmitting to the receivingend of the system the variations utilized at the receiver in the production of the image, the direct current component and very low frequency components being suppressed at the transmitter and compensation effected at the receiver. The receiving system includes a thermionic amplifier in t e out ut circuit of which is a glow discharge lamp to emit light of intensity varyin in accordance with the initial current. 0 receiving system also includes means for establishing the region of operation on the characteristic curve of the amplifier and the region of operation on the characteristic curve of the lamp independently, and means for indicating when the proper operating region on the amplifier characteristic is being employed. An attendant at the receiver is thus enabled -to reinsert the direct current component of the signal requisite for 'reproduction of the tone values of the subject with fidelity, by properly polarizing the lamp, and at the same time to adjust the amplifier to give the character of amplification best suited for distortionless overall transmission in the system.

Other objects and aspects of the invention will be apparent from the following description and claims:

Fig. 1 of the drawings is a schematic only one aperture at a time.

, co paratus at the transmitting end of the sys .tem. That apparatus comprises an are or constant intensity light source 3 andan optical system for causing a slender pencil of substantially parallel rays ofintense light derived from the arc to sweep across the region in front of the scanning ap aratus and scan the subject 1 in a series 0 successive parallel substantially horizontal lines. The optical system includes an opaque disc 4, which is'rotated at a speed 0 about 18 revolutions per second by a motor 5 and has a number of small circular apertures 6 arranged in a spiral extending around the disc near its rim. Two plano- 7 convex lenses 7 direct light from are 3 upon disc 4 so that an intense beam of lightpasses through each aperture as-the aperture moves across the illuminated area on the disc. An opaque screen 8 in front of the disc has a substantially rectangular opening 9 of such width as to transmit light from A lens 10' bends the slender pencil of substantially parallel rays passing through the aperture 85 and the opening 9 and forms an image of the moving aperture on the subject 1. As

a result of thls arrangement, the subject is completelrv scanned in a series of successive parallel ines by a small, rapidly moving 90 intensely bright s t of light once for each revolution of the 20.

It is not necessary that the subject be at the exact osition of the a rture images. The option system is such t at the slender beams of light sweeping across the region in front of the scanning apparatus just barely overlap each other even at a considerable distance from the apparatus. So, in this re pect, within wide l mits no confusion re- 1 sults as the subject moves toward or away from the apparatus. 1

As the spot of light passes over the subject, light is diffusely reflected from the sub ect, and a portion of the reflected light falls on one or more large photo-sensitive surfaces, such as the large photo-sensitive surface 11 of a large aperture photo-electric cell 12, and generates a picture current. The brightness of the image seen by the observer 2 at the receiving end of the s stem depends'upon the distance of the sub ect 1 from the photo-sensitive surface.

The scanning system described above is disclosed in more detail in the copending application of Frank Gray, Serial No. 227,619,. filed Oct. 21, 1927. The large a erture photo-electric cell having the large p oto-sensitive surface is disclosed in more detail in the copending application of G. R. Stilwell, Serial No. 181,552, filed April 6, 1927.

The picture current from the photo-electric device is am lified by an alternating current amplifier and the amplified current is transmitted through a transformer 14 to a line 15 or other transmission channel connecting the sending end of the system to the receiving end. At the receiving end of the system, the current from line 15 is transmitted through a transformer 16 and an amplifier A to an amplifier A including an electric s ace discharge amplifier tube 26 which fee s a neon glow discharge lamp 30. p

In front of the lamp is a disc 31 similar to the disc 4 and rotated synchronously with it by any suitable means (not shown). In front of the disc is an opaque screen 32 having an opening 33 of such size that only one of the apertures of disc 31 at a time is in the field of view of the observer 2. The lamp 30 is preferably of the type, disclosed more in detail in a copending application of Frank Gray, Serial No. 138,831, filed October 1, 1926, with a rectangular cathode 34 slightly larger than the field of view on the disc, the glow discharge covering the entire front surface of the cathode. The television field defined by the opening 33 and illuminated by light coming from lamp 30 through the moving apertures of disc 31, is viewed from in front of the disc without the aid of any optical system. The observer 2 sees at any instant a single aperture in the same relative position as the spot of light on the subject 1 at the transmitting end of the television system, and the brightness of the aperture corresponds to the amount of light reflected from that particular elemental area of the subject. ency of vision the observer 2 consequently sees an apparent image of the subject on the front surface of the disc 31.

Complete views of the subject are trans- On account of the persistfalls on the sensitive ce 1 during a nod of time covering the transmlsslon 0 several views, or in other words, durin a. period approximately equal to several flicker periods. By app ying a well-known mathematical principle, discovered by Fourier, to this varying light intensity, it'may be approximately considered as a constant intensity plus the sum of a series of sinusoidal components.

The constant component is really the average light intensity of the views, or a luminous field upon which the views occur as variations from the average light intensity. The expression lightround may be used to designate this uni orm field of avera e brightness. The current generated by tfie photo-electric cells is likewise a fluctuating direct current, which is the sum of a constant current, corresponding to the luminous light-ground, and a series of sinusoidal currents, corresponding to the variations from the light-ground.

The constant component or direct current component representin the light-ground could not be transmitte through amplifiers and transformers of commercial design and over telephone lines even if an amplifier could be designed for pro erly amplifying it to the requisite degree be ore putting it on the line 15. Moreover, the signals as generated by the photo-electric cells are ve minute, and adirect current amplifier that would amplify them to the requisite degree would not have the requisite stability. Therefore, the amplifier A (and also the amplifier constituted by amplifiers A and A) used to produce the requisite amount of amplification of these feeble signals is a vacuum tube amplifier embodying resistance-c0ndenser coupling circuits which prevent zero drift in the amplifier and give it the requisite stability. These coupling circuits are such that the amplifiers have a substantially constant efliciency over a frequency range extending from a frequency below the frame frequency of 18 cycles per second to a frequency above the picture element frequency, say 20,000 cycles per second. Such a coupling circuit, comprising a capacity 40 and a resistance 41, is shown coupling amplifiers A and A The values of capacity 40 and resistance 41 respectively,

may be, for example, 2 microfarads and 50,000 ohms.

However, pictures or views can not be reproduced with fidelity as regards tone value when the constant direct current represent- .ing the -.light-tone or light-ground of the picture :or view ise'liminated from the --picture cur-rent transmitted over thesystem until a correction which 'e-tiectively replaces this com )n'ent is made. --Forexample, ima ine it iat'the shaded squares and 60 in '1 ig .'2 are two types of pictures or views, or represent two aspects of a subject, which are'to-be transmitted by the system. .Substantially half of area-50 is constituted by a block .51, the tone of-which is light gray; and substantially half of area 50' is constituted by a block52, the tone of.which is medium gray. A block 61 liavin the same medium gray tone constitutes su stantially half of area 60; and substantially half of area 60 consists of-a block 62 dark gray in tone. At the. middle of the left hand edges ofareas 50 and 60 are rectangles 53 and 63, which "are black and. white, respectively; and at the middle of the lefthand edges of blocks 52 and 62 are rectangles 54 and 64, which are white and black, respectively. Each of these four rectangles is made of small .area comparedto one of the blocks such as 51, and narrow in the vertical direction, compared to a block such as 51. The relative dimensions, locations and tones of the various portionsof areas 50 and 60 have been. so chosen that, assuming the scanning spot to move in the verticaldirection in Fig. 2, when the spot tracesa path on area 50 indicated by dotted line 55 there is generated in the photo-electric cell a current wave 56 which is exactly like a current wave 66 correspondingly generated by a spot scanning along path 65' on area 60 as regards the alternating current components of the two waves, except for the narrow peaks.

57, 58, 67 and 68 created in these waves due to rectangles 53, 54, 63 and 64 respectively; and these narrow peaks have but a negligible effect in determining the average value of current for each wave. These waves 56 and path 55 or 65 as the case may be. Points on the curves correspond to horizontallyaligned points on the paths 55 and 65, as indicated by the horizontal projection lines connecting the curves with the paths. The current values for these waves are plotted toward the right from line as the reference line or line representing zero current value. The average value of current for wave 56 or the magnitude of the direct current component of the wave is indicated by line 59; and the average value of current for wave 66 or the magnitude of the direct current component of the wave is indicated by line 69. Since the area 50 is fairly light in general effect (has a bright light-ground),

whereas the area 66 is fairly dark in general efi'ect-(has a dark l1ght-ground), the magnitude of the direct current component of ternating current components of the waves 56 and 66 reach the grid of tube 26.

These received alternating' signal componentsare shown in Fig. -2 as voltage waves 56 and 66, respectively, with the axis or line of' zero voltage indicated at 59". lVaves 56and'66' are drawn each to the samescale as the other, since waves .56 and 66 are drawn each'to the same scale as the other.

Fig. 2 shows the grid voltage-plate current characteristic of tube 26. The straight portion, or range over which it will for the present be considered as desirable to operate, is the portion between points 81 and'82. The point 83 corresponds to a voltage just half way between the voltages corresponding to points 81 and 82, respectively, and would be the normal operating point of the tube for an average value of light-ground. Vertically aligned with this normal operating point isline 59 in Fig. 2*. This line corresponds to the average value (that is. the zero'value) of voltage for waves 56 and 66', respectively. If these waves were received by tube 26 when the grid biasing voltage of that tube had the value of the point 83, then the varying voltages on the grid, in the case of the two waves, would be the two voltages indicated by curves 56 and 66, respectively, and the operating region would be that determined by vertical projections from the curves of Fig. 2 on the curve of Fig. 2. With this value of grid bias the apparent images ofareas 50 and 60 as seen by observer 2 would be reproduced exactly alike. Areas 51 and 61 would have equal tone values, andjarcas 52 and 62 would have equal tone values. Furthermore, pcak 57 falls below the lower 1imit 81 of the assigned operating range, and peak 67 falls above the upper limit 82 of the assigned operating range.

The operating point 81 corresponds to zero signal amplitude at the transmitting end of the system. Therefore, if the direct current component of the initial signal had been transmitted, Eq would be the normal operating bias of the tube. Consequently, the operation about operating point 83 which results from the use of rid bias Eg is equivalent to the introduction of a uni-- directional voltage. component of the absolute value Eg,-.Eg,.

The distortions due, as explained above, .to the absence of the direct current component from the picture current received by amplifier A from amplifier A" and the effective reintroduction of a component of improper amplitude may be avoided or compensated for by varying the point about which operation takes place on the characteristic curve 80. To reproduce area 50 the grid bias should be altered as shown by curve 56 of Fig. 2", so that the average value of voltage is moved to the operating point 90. Under these conditions peaks 57 1 and 58 fall properly upon the limits 81 and 82, respectively, of the operating region of the characteristic. This alteration of the grid bias, to the value Eg has affected the reintroduction of the proper uni directional voltage component of the signal which is the absolute value Eg,--Eg

Similarly, to reproduce the area 60, the grid bias should be altered as shown by curve 66" of Fig. 2", so that the average value of the voltage is moved to the operating point 91. Under these conditions peaks 68 and 67" again fall upon the limits 81 and 82, respectively, of the operating region of the characteristic. This alteration of the grid bias, to value E has affooted the reintroduction of the proper direct current component of the signal which is the absolute value Eg,-Eg,.

In other words, if the direct current component had not been eliminated from the si nal, the normal tube bias would have been 191, which locates signal values corresponding to zero illumination at the lower limit 81 of the operating region of the characteristic of the tube. The reintroduction of the proper direct current components has therefore effectively shifted the operating bias with respect to alternating current components to the point E57 for the reproduction of area 50 and Eg, for the reproduction of area 60. The criterion of the proper adjustment is that peaks 57 and 68* fall on operating point 81 and peaks 58" and 67 fall on operating point 82. When alternating current wave 56' is delivered from amplifier A" to tube 26, the biasing voltage for the grid of tube 26 should be such that the variations of grid voltage which are caused by the wave occur about point 90 on characteristic 80 and the gain of tube 26 should be such that these variations coincide with the range between points 81 and 82. In other words, the wave 56' and the grid bias combined should appear on the grid as the wave 56" shown in Fig. 2", the average voltage value of wave 56", or the zero alternating voltage line being indicated by line 59 which is vertically aligned with point 90 of characteristic 80 of Fig. 2 as indicated by vertical projection lines extending from each figure toward the other.

Similarly, when alternating current wave 66' is delivered from amplifier A to tube 26, the biasing voltage for the grid of tube 26- should. be such that the variations of of Fig. 2 as indicated by vertical projection lines extending from Fig. 2 toward Fig. 2".

The desired gain for tube 26 can be obtained by proper adjustment of a gain control device comprising the resistance 41 in the input circuit of the tube and a contact 85 connected to the grid: of the tube and movable along the resistance 41. To accomplish the desired variations, mentioned above, of the operating point on characteristic 80, the observer 2 varies the negative grid potential of the tube 26 by means of acontact 87 movable into engagement with resistance taps 88 on a battery 86 which has its positive pole connected to the filament of the tube. The observer 2 can thus choose a light-ground to suit his own fancy by the value of the arbitrary direct current that he puts into the light cell 30, and he sees the original view or picture reproduced except that the luminous light-ground may not be the same as in the original if, in adjusting the grid bias, he must depend mere-. ly on hisfancy and his general ideas as to the nature of the object being viewed. Means for indicating the proper adjustment will be described presently.

Considering a period of time covering the transmission of a series of views comprising a large number of views, or in other words, considering a time period covering a large number of flicker periods, as the subjects move about or change in the particular series of views that is being sent, the average brightness of the field will vary slowly with time, and the receiving operator can vary the grid bias of the last tube at will, to suit his own fancy, or to accord with the indications of the above mentioned means for indicating the proper adjustment.

From the foregoing description it will be seen that the input of the last stage of the amplifier constituted by amplifiers A and A in tandem has a gain control device which determines the maximum amplitude of the alternating voltage applied to the grid; that the input also contains means for adjusting the grid bias to determine the operating point on the characteristic curve 80 of the amplifier; and that these two means together enable a region of the curve to be chosen for operation and enable the 'tion to a meshes and a'second battery or other source of uni- I directional voltage of value EQ. The source 97 may be termed the polarizing battery for the lam The resistance 96 may be of the order 0 ma nitude of the output impedance of the tu e. These elements in t e output circuit enable the illumination of the neon lamp to be varied linearly from zero illlllllilltltlOIL to different de rees. of illuminagpn for any. amplitude o incoming' signa The nature and par se of the various ads justments-described a ve will now be further explained with the assistance of Fi s. 2 and 2'. The solid line curve 100 of Fig. 2' is the operating characteristic curve of the neon lamp 30 plotted between voltages on the lamp as abscissae and the intensity of illumination of the lamp or the current through the lamp as ordinates. The voltage corresponding to point 100 is the striking voltage of the lamp. The curve 101 of Fig. 2 has ordinates corresponding to-those of amplifier characteristic 80 of Fig. 2, and

has abscissae corresponding to those of the neon lam characteristic 100 of Fig. 2'. Assume, or simplicity, that the incoming signal wave is the alternating current wave 66. The amplitude of the alternating current can be controlled bythe gain adjusting device to bring it within the desired range. It

is desired to o erate the amplifier over a linear portion 0 its characteristic 80 not only as regards the alternating current component of the signal but also to be able to vary the region operated over by the alternating current component on the characteristic curve to take care of difi'erent amounts of direct current componentwhich it is desired to introduce into the signal. It is further desired to control the up lication of volta e to the neon lamp 30 so that the lamp will be dark when the initial signal amplitude is zero and so that the brllliancy will vary linearly with the amplitude of the incoming signal.

Starting out with a given amplitudeof signal as indicated at 66' or 56' some point on the characteristic 80 is chosen as the lowest suitable 0 rating point from the standpoint of desired quality. The signal 66 is 'ven a certain amount of direct current bias which is shown by the line 69" in Fig. 2". The negative grid otential isthus chosen in accordance witi the criterion given above. If a different direct current component is desired, a difierent negative bias is chosen for the amplifier. For example, in the case of wave 56, having a large tween the extremes of the direct current com onent shall lie within the limits of a fair y linear portion of the characteristic curve 80. The amplifier rid bias is thus determined entirely from t e standpoint of the amplifier characteristic 80 without reference to the neon tube.

Turning now to the determination of the neon lamp bias, it is seen from the neon tube characteristic 100 that a certain voltage or bias, as indicated by the abscissa of point 81', is necessary to bring the lam up to the lowest illuminating voltage.-

s value of voltage should correspond to point 81 on curve 101, and the circuit constants should be so chosen that this voltage will be just equaled b the algebraic sum of the voltage E an the volta ance 96 corresponding to t e value of amplifier plate current indicated by point 81 at the lower end of the straight portion of characteristic v80. This value of voltage dro across resistance 96 is designated I R in ig. 2".

'When the circuit is adjusted in this manner and a signal is received representing blacks and grays, such a grid bias is used that the lower portion of the chosen range of characteristic 100is used, which changes the illumination of the lam from dark to dim. If the picture correspon to gray and white, such a grid bias is used that the up rend of the operating range of characteristic 100 is utilized and the neon lamp is illuminated all the time to a brilliant and less brilliant de gree.. In this manner the direct current component which was eliminated at the transmitter is reinserted, in effect, at the receiver.

The indicating means mentioned above comprises an amplifier tube 112 which has its grid and filament connected directly to the grid and filament respectivelyof tube 26 and has in its output circuit a resistance 113 and four neon glow discharge lamps A, B, C and D with polarizing batteries 115, 116, 117 and 118. Lam s A and B have their anodes connected to t e plate of tube 112, whereas lamps C and D have their cathodes connected to the plate of the tube. Due to persistenc of vision, lamps A and D appear lighted w en the adjustment of contacts 85 and 87 is correct, that is, when the variations of the space current of tube 112 coincide with the part of curve 80 extending from point 81 to point 82. If the range of the space current variations in tube 112 extends substantiall above point 82, lamp C appears The circuit constants for accomplishing these results may be, for example, as follows. The strikin voltage of each of the four neon lamps may 210 volts. Resistance 113 may be 2000 ohms. The space current of tube 112 corresponding to points 81 and 82 may be 5 milliamperes and 40 milliamperes, respectively, which will mean that the voltage .drops in resistance 113 corres o'nding to these oints are 10 volts and 80 v0 ts, respectively.

0 voltages of batteries 115, 116, 117 and 118 may be 125 volts, 10 volts, 215 volts and 10 volts respectively.

In Fig. 2, the intersection of the dotted lines extending from the lamps A, B, C and D, res ectively, with the curve 80 indicate in a qua itative way the points on the curve corres onding to the space currents of tube 112 w ich cause the voltage drops in resistance 113 to be such as, together with the voltages from the lam polarizing batteries 115 to 118, will cause t e. voltages across the respective lamps to equal the striking voltage of the lamps, that is, the voltage at which the lamps begin to glow when their voltage is gradually increased from a value insufiicient to cause the lamps to light. The lamp Ahas as its voltage the drop in resistance 113 and the voltage of the two batteries 117 and 118 in series, these batteries being so poled that their effect upon the lamp is diminished by the voltage drop in resistance 113. The lamp B has a smaller voltage since its voltage 15 the voltage of battery 117 diminished b the voltage drop in resistance 113. Lamp C has as its voltage the voltage drop in resistance 113 series aided by the voltage of battery 115. The lamp D has as its volta e the voltage drop in resistance 113 series aided by the voltages of the two batteries 115 and -116. Due to this arrangement lamps A and B are illuminated at the values of space current indicated and continue to low for all lower values. Lamps C and D fiecome illuminated at the values of space current shown and continue to glow for all higher values.

In the operation of this circuit, an attendant, or the observer 2, would need to know that the picture being transmitted, or the field being scanned at the transmitting end of the system, has some portions which vary substantially all the way between the extremes of white and black. He manipulates the gain and bias of the amplifier tube until the lamps A and D are illuminated, and the lamps B and C are dark. This assures that the full operating range of the amplifier characteristic is being covered but not exceeded in either direction. If lamp B, for example,

. is illuminated, the amplifier bias is too large and a point too far down on the amplifier characteristic is being used. If lamps B and C, for instance, are illuminated, it may be necessary to vary both the grid bias and the portion 64 in area 60, and some portion which 15 white, as for example, the portion 54 in area 50, or the portion 63 in area 60, such portions if not naturally present may be introduced in the subject being scanned or its background.

The copending a plication of H. E. Ives and Frank Gray erial No. 181,511, filed April 6, 1927, discloses in more detail the means suppressing the direct current compo-- nent of picture current at the transmitting end of a picture transmission system, and also discloses means for inserting a direct current component in the signal at the receiving end of the system.

What is claimed is:

1. In a signaling system, a glow discharge lamp of the type which emits light substantially proportional to the potential impressed upon it in excess of the striking voltage, a space discharge amplifier for supplying the lamp with fluctuating uni-directional voltage, and means to impress on said lamp adjustable values of steady potential equal to and greater than said striking volta e.

2. n a signaling system, a space discharge device having an anode, a cathode and a grid or impedance control element, an impedance included in the external space current circuit of said device, a source of space current, adjustable means connected to the grid and cathode for determinin the desired operating region on the amplifier characteristic curve, means to impress on the grid circuit signal variations to be amplified, a glow lamp connected to receive variable voltage developed across said impedance in response to variations in space current flow, and means in circuit with said glow lamp for impressing a steady voltage thereon.

3. In a signal receiving circuit for a picture transmission system, a three-electrode space discharge amplifier for the si nal variations, a neon glow lamp actuatef by the amplified signal variations, means for adjusting the amplifier to operate over a desired region of its space current-grid voltage characteristic and means for ap lying to said lamp a stead biasing potential equal to and in excess 0 its strikin volta e.

4. In a signaling system. an e ectric amp having a light producing characteristic substantially proportional to impressed voltage over a range of voltages the lowest of which is of a value substantially above zero, and means to impress upon said lamp voltages within saidrange, the voltages within said range being alone representative of the transmitted si nals, said means comprising a source of vo tage, a path for current from said source, and means connecting said lamp to said path and applying to said lamp a volta e different from that across said path.

5. n a signaling system, a receiving circuit comprising an electron discharge amplifier having an anode circuit, a source of current for said anode circuit, a glow discharge lamp in said anode circuit, and a current path for by-passing current around said lamp and a portion of said source, the

light emission from said lamp being sub-' stantially proportional to the voltage impressed thereon above the striking voltage.

6. The combination with an electric lamp which produces light only when the impressed voltage has a value substantially above zero, means for impressing a varying voltage u on said lamp, and a shunt circuit for said amp and a portion of said means in series.

7. The combination with an electric lamp which produces light only when the impressed voltage has a value substantially above zero, a source'o'f voltage for impressing a varying volta e upon said lamp, a path comprising sai lamp and a portion only of said source, and a shunt circuit for said path. 1

8. The combination with an electric lamp which produces light only when the impressed -voltage has a value substantially above zero, a source of voltage for impressing a varying volta e upon said lamp, a path comprising said lamp and a portion only of said source, and a shunt circuit for said path, said shunt path having substantially constant im edance for varyin impressed voltages a ove said light emitting volta e.

9. in a signaling system, a source of current comprising an amplifier having an anode circuit, a source of light and a voltage changing device connected in series with said anode circuit, light being produced only when the voltage impressed upon said light source has a value substantially above zero, and a path for shunting current around said lamp and said voltage changing device.

10. In an image transmission system, a, source of current comprising an electron discharge amplifier in which the currents in the output circuit corresponding to .the various light values of the bbject an image of which is to be produced have a range of amplitudes the lowermost of which has a value substantially above zero, a low discharge lamp having a striking vo tage corresponding to said lowermost current value, a voltage changing device connected to said lamp, and a shunt path for said lamp and saiddevice.

11. In an image receiver including a vacuum tube terminal amplifier, a receiving lamp, a source of voltage, and a current path, said current path bein connected in parallel with said receiving imp and said source of volta e across the output of said terminal ampli er.

12. A source of voltage, a pluralit of circuits supplied with voltage in para el from. said source,-a glow discharge lamp in one of said circuits, and an auxiliary source of voltage in one only of said circuits.

13.. A source of voltage, a plur lity of circuits supplied in parallel with vgllfage from said circuits, and means for maintainin the voltage across said glow lamp different rom the voltage across said other circuit. v 14. A source of unidirectional voltage having alternating components, a pluralit of circuits supplied in parallel with vo tage from said source, a glow discharge lamp in one of said circuits. and a source of volta e for maintainin different unidirectional-v0 tages across said lamp and said other circuit.

15. The method ofoperating a glow lamp from an electric space discharge device, which comprises, supplying the lamp with fluctuating unidirectional voltage. from the device and rendering the voltage across. the lamp different from .that supplied to .the lamp from the device.

16. A receiving system comprising a 1 low discharge device, an amplifier for amp if ying received picture currents and transmitdicating variations in the range of the'amplifier characteristic over which operation takes place.

17. A system for transmitting visual aspects of objectsto a distance, comprising means for generating a fluctuating unidirectional current representing the visual aspect of the object to be viewed at a dis tance means for deriving alternating current rom said unidirectional current, amplifying said alternating current and transmitting it to a distance a receiving amplifier for amplifying said transmitted current and combining therewith a unidirectional current, and means for indicating the value of the combining unidirectional current relative to the value of the direct current component of the first mentioned fluctuating unidirectional current.

18. In combination, a luralit of glow discharge lamps, a source or supp ying voltsaid source, a glow discharge lam in one of ting them to said device, and means for infying a signal having a 'direct current component, said system comprising. means for eliminating that component and amplifying another of the components of the signal, and 5 means included in said system for combining with the amplified other component direct current for restoring the original proportion between the direct component and the-other component. 19 In witness whereof, I hereunto subscribe my name this 6 day of April A. D.. 1927. JOSEPH W. HORTON.

fying a signal having a direct current com ponent, said system comprising eliminating that component an means for amplifying another of the components of the signal, and means included in said system for combining with the amplified other component direct current for restoring the original (Proportion between the direct component an the Y other component.

In witness whereof, I hereunto subscribe my name this 6 day of A ril A. D.. 1927.

Patent No. 1,728,122.

J OSEP W. HORTON.

JOSEPH W. HORTON.

It is hereby certified that error appears in the printed specifications of the above numbered patent requiring correction as follows: Page 7, beginning with line 130, strike out all to and including line 9, page 8, comprising claim 19, and insert the following as claim [9:

19. In a picture transmission system, means for generating picture currents having a direct current component, means for eliminating the direct current component from the picture current at a portion of the system, means for restoring the direct component at another portion of the system, and means for indicating the amount of the direct component restored.

And that the said Letters-Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 14th day' of November, A. D. 1933.

F. M. Hopkins (Seal) Acting Commissioner of Patents. 

